I had a strange problem come up yesterday with my 360, and I'm wondering if it's a common, or at least known problem. It froze up on me a couple times (about an hour or so apart) and when I shut it down and restarted it the second time, a message came up on the screen saying "Mode not supported". It's an HDMI-enabled model, and I was thinking maybe the HDMI cable was loose or something. But after checking and rechecking all the connections, it still wasn't coming up on my TV.
Then I thought (and hoped) it was just a problem with the HDMI cable. I have a PS3 hooked up to the same set, also via HDMI. I've tried switching the cables for each system, and I've tried plugging each one into different HDMI inputs on the TV. The PS3 comes up fine with either source and either cable; the 360 gets the "Mode not supported" message no matter which cable or input is used. So I've concluded that the problem is with the 360 itself, for whatever reason, it's suddenly not working with HDMI.
Not sure if this matters, but the first time it froze yesterday I wasn't able to shut the system off with the controller, or by pushing the power button on the front. I eventually had to unplug the power-brick, then replug it in. When the "Mode not supported" problem first came up, I thought it might just need to reset itself after being shut down that way. Anyway, after I plugged it back in, I played a game of NBA 2K8, everything was fine, and then after I popped the disc out, it froze again when I was just on the dashboard.
Anybody have any idea if there's a simple fix for this? I'm thinking I'm probably going to have to send it in and pay Microsoft to repair it. Thanks for any help or advice.